The present invention is in the field of ceramic sealing, and particularly relates to an improved method and apparatus for dispensing fritted solder glasses useful for sealing together glass or other ceramic parts.
Sealing glass compositions such as suspensions of fritted solder glasses are generally referred to in the industry as "frit" and are used in the fabrication of many different kinds of assemblies comprising ceramic parts, glass envelopes for electrical devices, glass-ceramic components for telescope mirror blanks, and ceramic substrates for electrical circuits. One major sealing application of frit is in the manufacture of cathode ray tube envelopes for television picture tubes and the like. Such envelopes are fabricated by sealing a funnel member and a face plate or panel member together through the utilization of a frit which is normally applied by extrusion in the shape of a continuous ribbon or bead on at least one of the mating or sealing surfaces provided on the panel and funnel. Such parts are then joined together and fired to provide an integral assembly wherein the frit provides a mechanically strong hermetically sealed joint.
In the past it has been customary to apply a bead of such frit material to the sealing edge of an article to be sealed by means of an up-right cylindrical type container having an orifice adjacent the bottom and a supply of the frit material to be dispensed retained therein under a constant pneumatic pressure. However, due to the fact that the frit retained within such cylinder changes viscosity with time and temperature and further in view of the fact that the head of the frit material varies as the frit is used up under pressure, the amount of frit layed down by such known dispensers tended to vary over a wide range, thus producing unacceptable seal strengths either due to a lack or an excess of frit material. Further, in order that the frit material will not run over the seal edge of the glass article and also to provide for a shaped cross-section with more frit on the inside which after firing results in a stronger seal, it is desirable to dispense a fairly high viscosity frit material with a shaped cross section. However, with conventional constant pressure dispensers, the necessary high viscosity frit materials could not be conveniently dispensed, since the required high pressures merely blew a hole through the center of the frit paste adjacent the dispensing orifice.
It thus has been a principal object of the present invention to provide method and apparatus for dispensing a uniform amount of frit for sealing glass articles, independently of its temperature or viscosity, by utilizing a controlled constant volume displacement.